Eric Sembrat's Test Bonanza

Abstract: An important frontier of research in metrology is the development of techniques to surpass the standard quantum limit using quantum squeezed states or other entangled states. In this talk, we report the first observation of squeezed ground states generation in an 87Rb spinor condensate [1]. The measurement of squeezed ground states builds on previous experiments of spin-nematic squeezing [2]. A spin-1 Bose-Einstein condensate is tuned near the quantum critical point between the polar and ferromagnetic quantum phases to create a ground state with squeezing properties. In contrast to typical non-equilibrium methods for preparing atomic squeezed states by quenching through a quantum phase transition [2], squeezed ground states are time-stationary and remain squeezed for the lifetime of the condensate. A squeezed ground state with a metrological improvement up to 6 − 8 dB and a constant squeezing angle maintained over 2 s is demonstrated.

A protocol consisting of a pair of controlled quenches of an external magnetic field is applied, which allows fast tuning of the system Hamiltonian in the vicinity of a phase transition [3]. Our protocol effectively shortcuts the adiabatic technique, overcoming the challenge of maintaining adiabaticity in the neighborhood of the quantum critical point where the frequency scale of the final Hamiltonian evolution tends to zero. This protocol is indicative of creating eigenstates of the system through the non-adiabatic method and lay the foundation for future experiments involving entangled eigenstates generation.

Reference:

[1] L. Xin, M. Barrios, J. T. Cohen, and M. S. Chapman, “Squeezed ground states in a spin-1 bose-einstein condensate,” arXiv.2202.12338, 2022.

[2] C. D. Hamley, C. S. Gerving, T. M. Hoang, E. M. Bookjans, and M. S. Chapman. Spin-nematic squeezed vacuum in a quantum gas. Nature Physics, 8(4):305–308, 2012.

[3] L. Xin, M. S. Chapman, and T. A. B. Kennedy, “Fast generation of time-stationary spin-1 squeezed states by nonadiabatic control,” PRX Quantum, vol. 3, p. 010 328, 1 Feb. 2022.

Motivated by observational searches for potential gravitational-wave (GW) signals from massive black binary (MBHB) coalescences, we developed a model to describe orbital evolution of MBHBs. In this thesis, we use the model developed to determine how the properties of the merger remnant galaxy and the orbital configuration of MBHs affect the likelihood for and timescale to a coalescence. By varying galactic properties and orbital configurations of MBHBs in the model, we built a parameter space that contains 40,000 model galaxies, spans a wide range in initial orbital eccentricities and includes both prograde and retrograde orbits. We used these models to acquire a comprehensive view of how different types of orbital decay mechanisms impact the MBHB evolution. We estimated the LISA detection rates for different binary orbital configurations in the absence and presence of radiation feedback and explored the properties of MBHBs that are most likely to be detected as GW sources by applying the model on MBH pairs from the IllustrisTNG simulation. Finally, we use the model to quantify the electromagnetic (EM) detectability of dual active galactic nuclei (dAGNs). By tracking how the EM detectability varies with galaxy and orbital properties, we provided a convenient way to select dAGN candidates that evolve into GW sources. These kinds of predictions will be crucial for the future and present EM and GW observatories, for they will indicate where to look for possible MBH coalescences or the most detectable dAGNs.

Abstract

Single-cell measurements of mRNA copy numbers inform our understanding of stochastic gene expression, but these measurements coarse-grain over the individual copies of the gene, where transcription and its regulation take place stochastically. We recently combined single-molecule quantification of mRNA and gene loci to measure the transcriptional activity of an endogenous gene in individual Escherichia coli bacteria. When interpreted using a theoretical model for mRNA dynamics, the single-cell data allowed us to obtain the probabilistic rates of promoter switching, transcription initiation and elongation, mRNA release and degradation. Unexpectedly, we found that gene activity is strongly coupled to the transcriptional state of another copy of the same gene present in the cell, and to the progression of the bacterial cell cycle. These gene-copy and cell-cycle correlations demonstrate the limits of mapping whole-cell mRNA numbers to the underlying stochastic gene activity and highlight the contribution of previously hidden variables to the observed population heterogeneity.

Abstract: Cell adhesion and migration are essential to fundamental processes throughout the lifespan of multicellular organisms, including in embryonic development, tissue maintenance, and disease. Over the past several decades, researchers have established a deep molecular understanding of the mechanisms governing the attachment of cells to the extracellular matrix (ECM) through assemblies of adhesion proteins at the cell-ECM interface. However, sizable sugars and glycoproteins residing at the very same cell-ECM interface may also play an important yet unrecognized mechanical role in the regulation of cell adhesion and migration. Hyaluronan (HA), a giant sugar synthesized on the cell membrane by the HA synthase family is often confined at the cell-ECM interface as part of the membrane-bound HA-rich glycocalyx or embedded into macromolecular structures in the ECM. We hypothesized that confined HA at the cell-ECM interface is compressed, and the consequent repulsion may counteract adhesive forces to decrease the effective cell adhesion strength, and thereby modulate cell migration speed. We explored the potential biomechanical role of HA in vitro, ex vivo and in vivo, by manipulating cells to change the levels of interfacial HA and by quantifying the resulting cell morphology, adhesion, and migration responses. We then compared our results with polymer physics-based theoretical predictions and integrated them into experiment-driven models that predicted the repulsion force by compressed HA at the interface as well as HA-induced membrane configurations at the dorsal and ventral sides of the cell. Taken together, our results suggest another layer of regulation by HA exists in the molecular mechanisms governing cell adhesion and migration and they emphasize the hidden mechanical role sugars may play in other biological processes.